The present invention relates to the field of food extrusion, and more particularly to a device for sensing and indicating the pressure within a food extruder.
The advent of high output food extruders, capable of cooking and expanding proteinaceous and farinaceous materials, proved a boon to pet food and cereal manufacturers. However, sensing pressure within these devices has been complicated by the fact that there has to this date been no reliable device capable of sensing the pressure within an extruder operating on a continuous basis over extended periods of time. The devices which have been known are susceptible to caking and embedding with the farinaceous and proteinaceous materials being extruded. Because of this, scientific studies designed to deduce the variation of product qualities and processing efficiencies as function of process pressure, have been difficult to impossible to run.
Pressure sensing devices known for use in plastics extruders have not been successful when applied to food extruders because of the different nature of the materials being plasticized. Fouling of the pressure sensors in plastics extruders is minimal due to the thermoplastic nature of the materials involved. Thus, in a plastics extrusion situation, the thermoplastic material will be in a constant state of melt and will not cool down to set up within the extruder. In the food extruder, on the other hand, the proteinaceous and farinaceous materials pass through a thermoplastic state into a thermosetting state where they tend to coagulate and heat set.
There is a present need for a system which would enable measuring pressure within the extruder barrel on a continuous basis. The nature of the food material is such that a simple Bourdon tube gage cannot be used because the opening to the internal oval tube is quickly plugged by the food material being processed. Moreover, differential pressure instruments utilizing diaphrams cannot be employed because of the heat-setting character of the food material at high temperature which tends to cause it to cake on the diaphram, rendering it insensitive. Thus, what is needed is a pressure sensing and measuring device which is insensistive to caking of the food material being extruded.